A thermocouple is provided in an industrial plant, and the temperature information obtained from the thermocouple is used as an index for evaluating the performance of the industrial plant. The thermo-electromotive force generated by the thermocouple is inputted into a monitoring and control apparatus so as to be used for temperature monitoring and temperature control.
The thermocouple is gradually deteriorated by being subjected to stress due to repeated expansion and contraction caused by temperature change. The thermocouple is provided with a system for detecting the deterioration thereof. When the deterioration of the thermocouple is detected by the system, a measure, such as exchanging the thermocouple, is taken by plant maintenance personnel.
As an example of the conventional detection system, a detection system provided with two active and standby thermocouples is known. The conventional detection system has such a merit that an abnormality of the standby side thermocouple can be monitored by monitoring the difference between the detection signals of the two thermocouples.